The hydrolysis and sequencing of proteins by Co(III) complexes coordinated to tetradentate ligands is being studied. Variation of the nature of the tetradentate ligand changes the substitution lability of the coordinated water molecules and thus the substitution rate at the N-terminal peptide residue. The effect of the amino acid side chain structure on the rate of hydrolysis of the peptide is being investigated. A sequencing method based on the sustained release of amino acid residues is being developed.